The embodiment relates to a light emitting device, a method of fabricating the same, a light emitting device package, and a lighting system.
Since a nitride semiconductor represents higher thermal stability and wider bandgap energy, the nitride semiconductor attracts great attention in development of an optical device and a high-power electronic device. In particular, blue, green, and UV light emitting devices comprising the nitride semiconductor have been commercialized and extensively used.
The efficiency of the light emitting device is mainly divided into external light emission efficiency and internal light emission efficiency. Among them, the external light emission efficiency refers to the probability of outputting a light from an active layer to the outside of a device, and has a restricted value due to the total reflection caused by the difference in the refractive index between a semiconductor layer and air or a background material such as epoxy.
In order to improve the external light emission efficiency, two concepts may be taken into consideration. First, a scheme of employing the roughness structure or the periodical concave-convex structure for the interface of the semiconductor layer may be taken into consideration. Second, resonant cavity effect may be used likewise a resonant cavity LED.
When the interface of the semiconductor layer is deformed by the roughness structure or the periodical concave-convex structure, the light confined due to the total reflection can be extracted to the outside.
In contrast, when the resonant cavity effect is used, the direction of the light emitted from the active layer is adjusted through an intrinsic mode of the resonant cavity, so that light extraction efficiency can be improved and the directionality of the light can be adjusted.